Composite photoresist for pattern transferring

ABSTRACT

A composite photoresist structure includes an first organic layer located on a substrate, a sacrificial layer located on the first organic layer, and a second organic layer located on the sacrificial layer. The first organic layer is made of materials that can be easily removed by plasma. Therefore, the surface of the substrate will not be damaged while transferring a predetermined pattern onto the substrate.

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a photoresist structure, and more particularly, to a photoresist structure suitable for sub-micron pattern transfers in semiconductor processes.

[0003] 2. Description of the Prior Art

[0004] Generally, integrated circuit production relies on the use of photolithographic processes and etching processes to define various electrical elements and interconnecting structures on microelectronic devices. With the coming of a generation of Ultra Large Scale Integrated (ULSI) Circuits, the integration of semiconductor devices has gotten larger and larger. G-line (436 nm) and I-line (365 nm) wavelengths of light have been widely used in photolithography processes. However, in order to achieve smaller dimensions of resolution, wavelengths of light used for photolithography processes have been reduced into deep UV regions of 248 nm and 193 nm. Nevertheless, the shorter the wavelengths of light are, the thinner the photoresist layers are. The thin photoresist layers might not be thick enough for blocking the etching processes in the following fabrication. As a result, for a photolithography process utilizing short wavelengths of light, it is necessary to look for a photoresist structure suitable for lithography processes and etching processes.

[0005] Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior art photoresist structure. As shown in FIG. 1, a semiconductor wafer 10 comprises a substrate 12, an anti-reflection layer 14, and a photoresist layer 16. Because wavelengths of light used for exposure processes are related to the depth of focus (DOF), a required thickness of the photoresist layer 16 depends on the wavelengths of light. Accordingly, the thickness of the photoresist layer 16 has to be thin enough so that the molecules in the surface of the photoresist layer have approximately the same focus as the molecules in the bottom of the photoresist layer. However, the photoresist layer 16 is used to be a hard mask on the substrate 12 in the following etching processes. For this reason, the thin photoresist layers might not be thick enough for blocking the following etching processes.

[0006] Please refer to FIG. 2. FIG. 2 is a schematic diagram of another prior art photoresist structure used to overcome the above-mentioned problem. As shown in FIG. 2, a semiconductor wafer 20 comprises a substrate 22, a silicon oxynitride layer 24, an anti-reflection layer 26, and a photoresist layer 28. Therein the silicon oxynitride layer 24 serves as a hard mask so that the photoresist layer 28 together with the silicon oxynitride layer 24 can block the etching processes in the following fabrication. After the predetermined pattern of the mask is transferred onto the substrate 22, the silicon oxynitride layer 24, the anti-reflection layer 26, and the photoresist layer 28 are removed. However, the silicon nitride layer 24 is not easy to etch away. Thus, the process of removing the silicon nitride layer 24 usually causes damage to the surface of the substrate 22.

[0007] In addition, methods used to overcome the above-mentioned problem further include bilayer photoresist technology (U.S. Pat. No. 6,323,287) and top surface image (TSI) technology (U.S. Pat. No. 6,296,989). However, both of the two methods require new photoresist materials. For example, the photoresist layer used in the TSI technology comprises silicon-containing materials. Providing new photoresist materials will increase production costs and increase complexity and difficulty of processes. As a result, it is necessary to look for a photoresist structure suitable for sub-micron pattern transfers in photolithography processes and etching processes.

SUMMARY OF INVENTION

[0008] It is therefore a primary objective of the claimed invention to provide a composite photoresist structure so as to solve the above-mentioned problem.

[0009] According to the claimed invention, a composite photoresist structure includes a first organic layer located on a substrate, a sacrificial layer located on the first organic layer, and a second organic layer located on the sacrificial layer. The first organic layer is made of materials that can be easily removed by plasma. Therefore, the surface of the substrate will not be damaged while transferring a predetermined pattern onto the substrate.

[0010] It is an advantage over the prior art that the claimed invention provides a composite photoresist structure including a first organic layer, an inorganic sacrificial layer, and a second organic layer. A thickness of the second organic layer can be adjusted according to wavelengths of light sources used in exposure processes. Simultaneously, by adjusting thicknesses of the sacrificial layer and the first organic layer, the composite photoresist structure is thick enough to block following etching processes. Thus, the claimed photoresist structure is suitable for sub-micron pattern transfers in semiconductor processes. In addition, the first organic layer is regarded as a hard mask and it is easily removed by use of plasma. It is a further advantage that removing the first organic layer will not damage the substrate.

[0011] These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the multiple figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0012]FIG. 1 is a schematic diagram of a prior art photoresist structure.

[0013]FIG. 2 is a schematic diagram of another prior art photoresist structure.

[0014]FIG. 3 is a schematic diagram of a composite photoresist structure according to the present invention.

[0015]FIG. 4A to FIG. 4F are schematic diagrams illustrating an etching process utilizing the composite photoresist structure.

[0016]FIG. 5 is a schematic diagram of a composite photoresist structure according to another embodiment of the present invention.

DETAILED DESCRIPTION

[0017] Please refer to FIG. 3. FIG. 3 is a schematic diagram of a composite photoresist structure according to the preferred embodiment of the present invention. As shown in FIG. 3, a composite photoresist structure 30 comprises a first organic layer 30 a, a sacrificial layer 30 b located on the first organic layer 30 a, and a second organic layer 30 c located on the sacrificial layer 30 b . The first organic layer 30 a and the second organic layer 30 c both comprise organic materials. The sacrificial layer 30 b comprises inorganic materials.

[0018] In particular, the first organic layer 30 a is made of low dielectric organic materials, such as SiLK™. Additionally, the first organic layer 30 a is also made of spin-on glass (SOG). Consequently, it is easy to remove the first organic layer 30 a by means of plasma, which includes oxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon (Ar), C_(X)F_(y), C_(x)H_(y)F_(z), or helium (He) plasma. The sacrificial layer 30 b is made of inorganic anti-reflection materials such as silicon oxynitride (SiON) and silicon nitride (SiN). In addition, the sacrificial layer 30 b is also made of materials used for conventional hard masks, such as silicon nitride and silicon oxide. Moreover, the second organic layer 30 c is made of organic photoresist materials that include positive photoresist materials and negative photoresist materials. Furthermore, the second organic layer 30 c is made of organic materials suitable for utilizing in the e-beam lithography process. Noticeably, the composite photoresist structure 30 is suitable for any photolithography processes in the semiconductor fabrication. It should be known by one skilled in the art that a thickness of each of the first organic layer 30 a, the sacrificial layer 30 b, and the second organic layer 30 c could be adjusted according to requirements of processes.

[0019] Please refer to FIG. 4A to FIG. 4F. FIG. 4A to FIG. 4F are schematic diagrams illustrating an etching process utilizing the composite photoresist structure 30. As shown in FIG. 4A, a semiconductor wafer 40 comprises a substrate 42 and the composite photoresist structure 30 formed on the substrate 42. The substrate 42 is a silicon substrate, a metal substrate or a dielectric layer. Firstly, as shown in FIG. 4B and FIG. 4C, an exposure process and a development process are performed to transfer a predetermined pattern onto the second organic layer 30 c. Then, using the second organic layer 30 c as an etching mask, a dry etching process is performed on the sacrificial layer 30 b in order to transfer the predetermined pattern in the second organic layer 30 c onto the sacrificial layer 30 b. Besides, in another embodiment of the present invention, the predetermined pattern can be formed in the second organic layer by utilizing the e-beam lithography process.

[0020] As shown in FIG. 4D to FIG. 4F, utilizing the sacrificial layer 30 b to be an etching mask, an anisotropic etching process is performed to transfer the predetermined pattern onto the first organic layer 30 b. Then, using the sacrificial layer 30 b and the first organic layer 30 a as an etching mask, an etching process is performed to transfer the predetermined pattern in the first organic layer 30 a onto the substrate 42. While etching the substrate 42, the sacrificial layer 30 b is removed concurrently. After transferring the predetermined pattern onto the substrate 42, the first organic layer 30 a is subsequently removed. Up to now, the predetermined pattern on the mask is thoroughly transferred onto the substrate 42. The first organic layer 30 a is regarded as a hard mask, and its thickness can be adjusted in order to block subsequent etching processes. Thus, the composite photoresist structure 30 can be used in a photolithography process utilizing light sources with wavelengths shorter than 248 nm in deep UV regions. Furthermore, conventional hard masks are generally made out of silicon nitride or silicon oxide, which are not easy to etch away. Hence, an acidic trough is required to remove the conventional hard masks. Conversely, it is easy to remove the first organic layer 30 a through use of plasma. Furthermore, removing the first organic layer 30 a will not damage the substrate 42.

[0021] Please refer to FIG. 5. FIG. 5 is a schematic diagram of a composite photoresist structure according to another embodiment of the present invention. As shown in FIG. 5, a composite photoresist structure 50 comprises a first organic layer 50 a, a sacrificial layer 50 b located on the first organic layer 50 a, an anti-reflection layer 50 c located on the sacrificial layer 50 b, and a second organic layer 50 d located on the anti-reflection layer 50 c. The first organic layer 50 a, is made of low dielectric organic materials. In addition, the first organic layer 50 a, can be made of spin-on glass (SOG). It is easy to remove the first organic layer 50 a, by use of plasma. The sacrificial layer 50 b is made of materials used for hard masks such as silicon nitride and silicon oxide. The anti-reflection layer 50 c is made of organic materials used for organic bottom anti-reflection coating such as polyimide and the like. Additionally, the anti-reflection layer 50 c can also be made of inorganic materials used for inorganic bottom anti-reflection coating such as silicon oxynitride (SiON). The anti-reflection layer 50 c can prevent incident light from reflecting from the substrate to the composite photoresist structure 50. Thus, due to the anti-reflection layer 50 c, forming a standing wave in the second organic layer 50 d is avoided. The second organic layer 50 d is made of organic photoresist materials that comprise positive photoresist materials and negative photoresist materials. As mentioned above, the composite photoresist structure 50 can be utilized in any photolithography processes. It should be known by one skilled in the art that a thickness of each of the first organic layer 50 a, the sacrificial layer 50 b, the anti-reflection layer 50 c, and the second organic layer 50 d could be adjusted according to requirements of processes.

[0022] In comparison with the prior art, the present invention provides a composite photoresist structure including a first organic layer, an inorganic sacrificial layer, and a second organic layer. A thickness of the second organic layer could be adjusted according to wavelengths of light sources used in exposure processes. Simultaneously, by adjusting thicknesses of the sacrificial layer and the first organic layer, the composite photoresist structure is thick enough to blockensuing etching processes. Thus, the claimed photoresist structure is suitable for sub-micron pattern transfers in semiconductor processes. As a result, the predetermined pattern of the mask can be accurately transferred onto the semiconductor wafer, and a critical dimension (CD) is therefore controlled well. In addition, the first organic layer is regarded as a hard mask and it is easily removed through use of plasma. It is also an advantage that removing the first organic layer will not damage the substrate.

[0023] Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bound of the appended claims. 

What is claimed is:
 1. A composite photoresist structure, comprising: a first organic layer disposed over a surface to be etched; a sacrificial layer disposed on the first organic layer; and a second organic layer disposed on the sacrificial layer.
 2. The composite photoresist structure of claim 1 wherein the surface is selected from the group consisting of a silicon surface, a metal surface, and a dielectric layer surface.
 3. The composite photoresist structure of claim 1 wherein the first organic layer is made of an organic material that is easy to be removed by means of plasma, thereby avoiding damage of the surface to be etched during a pattern transferring process.
 4. The composite photoresist structure of claim 3 wherein the first organic layer is made of low dielectric organic materials.
 5. The composite photoresist structure of claim 3 wherein the first organic layer is made of SOG.
 6. The composite photoresist structure of claim 3 wherein the plasma is selected from the group consisting of oxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon (Ar), C_(x)F_(y), C_(x)H_(y)F_(z), and helium (He) plasma.
 7. The composite photoresist structure of claim 1 wherein the sacrificial layer is made of inorganic anti-reflection materials.
 8. The composite photoresist structure of claim 1 wherein the sacrificial layer is made of a material selected from the group consisting of silicon nitride, silicon oxide, and silicon oxynitride.
 9. The composite photoresist structure of claim 1 wherein the second organic layer is made of an organic photoresist material capable of absorbing light with a wavelength of 248 nm and the less.
 10. The composite photoresist structure of claim 1 wherein the second organic layer is suitable for an e-beam lithography process.
 11. A photoresist structure, suitable for sub-micron pattern transfers in semiconductor processes, the photoresist structure comprising: a first organic layer disposed over a surface to be etched; a sacrificial layer disposed on the organic layer; an anti-reflection layer disposed on the sacrificial layer; and a second organic layer disposed on the anti-reflection layer.
 12. The photoresist structure of claim 11 wherein the surface is selected from the group consisting of a silicon surface, a metal surface, and a dielectric layer surface.
 13. The photoresist structure of claim 11 wherein the first organic layer is made of an organic material that is easy to be removed by means of plasma, thereby avoiding damage of the surface to be etched during a pattern transferring process.
 14. The photoresist structure of claim 13 wherein the first organic layer is made of a material selected from the group consisting of low dielectric organic materials and SOG.
 15. The photoresist structure of claim 13 wherein the plasma is selected from the group consisting of oxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon (Ar), C_(x)F_(y), C_(x)H_(y)F_(z), and helium (He) plasma.
 16. The photoresist structure of claim 11 wherein the sacrificial layer is made of a material selected from the group consisting of silicon nitride and silicon oxide.
 17. The photoresist structure of claim 11 wherein the anti-reflection layer is made of organic anti-reflection materials.
 18. The photoresist structure of claim 17 wherein the anti-reflection layer is made of polyimide.
 19. The photoresist structure of claim 11 wherein the anti-reflection layer is made of inorganic anti-reflection materials.
 20. The photoresist structure of claim 19 wherein the anti-reflection layer is made of a material selected from the group consisting of silicon nitride and silicon oxynitride.
 21. The photoresist structure of claim 11 wherein the sacrificial layer is removed during a predetermined pattern being transferred to the surface to be etched, while the first organic layer is removed after the predetermined pattern is transferred into the surface to be etched.
 22. The photoresist structure of claim 11 wherein the second organic layer is made of an organic photoresist material capable of absorbing light with a wavelength of 248 nm and the less.
 23. The photoresist structure of claim 11 wherein the second organic layer is suitable for an e-beam lithography process.
 24. A method of fabricating a semiconductor device comprising: providing a substrate; sequentially forming a first organic layer, a sacrificial layer, and a second organic layer on the substrate; performing a photolithography process so as to form a predetermined pattern in the second organic layer; utilizing the second organic layer as an etching mask for etching the sacrificial layer till a surface of the first organic layer is exposed, thus the predetermined pattern being transferred to the sacrificial layer; utilizing the sacrificial layer as an etching mask for etching the first organic layer till a surface of the substrate is exposed, thereby the predetermined pattern being transferred to the first organic layer; utilizing the sacrificial layer and the first organic layer as an etching mask for etching the substrate, thereby transferring the predetermined pattern to the substrate; removing the first organic layer by use of plasma.
 25. The method of claim 24 wherein the first organic layer is made of a material selected from the group consisting of low dielectric organic materials and SOG.
 26. The method of claim 24 wherein the plasma is selected from the group consisting of oxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon (Ar), C_(x)F_(y), C_(x)H_(y)F_(z), and helium (He) plasma.
 27. The method of claim 24 wherein the sacrificial layer is made of a material selected from the group consisting of silicon nitride and silicon oxide.
 28. The method of claim 24 wherein the second organic layer is made of an organic photoresist material capable of absorbing light with a wavelength of 248 nm and the less.
 29. The method of claim 24 wherein the second organic layer is suitable for an e-beam lithography process.
 30. The method of claim 24 wherein the substrate is selected from the group consisting of a silicon substrate, a metal substrate, and a dielectric layer. 